Bone screw

ABSTRACT

A bone screw having a screw member possessing a threaded section and a head and a receiving part at the head end for receiving a rod to be connected to the bone screw is provided. The receiving part has on open first bore and a substantially U-shaped cross-section having two free legs provided with a thread. Furthermore, the receiving part has a second bore on the end opposite to the first bore whose diameter is greater than that of the threaded section and smaller than that of the head. On the bottom of the first bore a seat for the head is provided. In order that the screw member can be pivoted to at least one side by an enlarged angle, the edge bounding the free end of the second bore viewed relative to the axis of the first bore is of asymmetric construction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/299,189, filed Oct. 20, 2016, which is a continuation of U.S.application Ser. No. 14/488,730, filed Sep. 17, 2014, now U.S. Pat. No.9,498,256, which is a continuation of U.S. application Ser. No.12/982,728, filed Dec. 30, 2010, now U.S. Pat. No. 8,864,803, which is acontinuation of U.S. application Ser. No. 11/319,427, filed Dec. 29,2005 which is a continuation of U.S. application Ser. No. 10/763,431,filed Jan. 22, 2004, now U.S. Pat. No. 8,409,260, which is acontinuation of U.S. application Ser. No. 10/037,698, filed Nov. 9,2001, now U.S. Pat. No. 6,736,820, which claims the priority of GermanPatent Application No. 100 65 397.9, filed on Dec. 27, 2000 and GermanPatent Application No. 100 55 888.7, filed on Nov. 10, 2000, thedisclosures of each of which are incorporated herein by reference.

FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a bone screw having a threaded section and ahead and a receiving part at the head end for receiving a rod to beconnected to the bone screw, the receiving part possessing an open firstbore and a substantially U-shaped cross-section having two free legsprovided with a thread and a second bore at the end opposite to thefirst bore, whose diameter is greater than that of the threaded sectionand smaller than that of the head and which forms the seat for the head,and a nut or screw working together with the thread.

Such a bone screw is disclosed, for example, in U.S. Pat. No. 5,672,176.In the known bone screw the head is of spherical segment-shapedconstruction. The bottom of the first bore adjacent to the second boreis likewise of spherical segment-shaped construction so that thespherical head lies on this spherical section. The plane going throughthe bounding edge is oriented at right angles to the axis of the firstbore and the mid-point of the second bore coincides with the axis of thefirst bore. By this means it is achieved that the threaded sectionpossessing the head is pivotable in a predetermined angle of generallyup to 25° about the axis of the first bore so that even after screwingthe threaded section into a vertebral segment orientation of thereceiving part receiving a rod is possible. At the same time, the sizeof the pivot angle is limited to the extent that the second bore as afunction of the diameter of the head must not exceed d certain size sothat the head still has an adequate hold in the receiving part.

The use of such bone screws is something of a problem in the region ofcervical vertebrae. In this case, due to the small dimensions of thecervical vertebrae, it is necessary that the screws must always bepivoted to one side and upwards, a greater degree of pivoting beingnecessary than is the case in the larger thoracic vertebrae and lumbarvertebrae.

SUMMARY OF THE INVENTION

The aim of the invention is to provide a bone screw which permits alarger pivot angle. This task is solved by a bone screw having a screwmember that possess a threaded section, a head and a receiving part atthe head end for receiving a rod to be connected to the bone screw. Thereceiving part has an open first bore and a substantially U-shapedcross-section having two free legs provided with threads, a second boreat the end opposite the first bore having a diameter greater than thediameter of the threaded section and smaller than the diameter of thehead, and a seat for the head and a nut or screw acting together withthe thread. When viewed relative to the axis of the first bore, the edgebounding the free end of the second bore is asymmetrical.

Refinements of the invention are identified in the more detailedembodiments described below.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and practical advantages of the invention emerge fromthe description of exemplified embodiments with reference to thefigures.

FIG. 1 depicts a side elevation of a first embodiment of the invention,partly in sectional representation.

FIG. 2 shows an enlarged detail of FIG. 1.

FIG. 3 depicts a side elevation, partly in sectional representation, ofa second embodiment of the invention.

FIG. 4 depicts a corresponding representation of a further embodiment ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION

The bone screw includes a screw member proper 1 having a threadedsection 2 and a head 3. The head is formed in the shape of a segment ofa sphere in the region adjoining the threaded section. Coaxial with thethread axis and on the end opposite to the threaded section 2 the headpossesses a recess 4 for engagement with a socket screw key.

The bone screw further comprises a cylindrically constructed receivingpart 5. At one end this has a first bore 6 of axially symmetricalconstruction. On the opposite end a second bore 7 is provided whosediameter is greater than that of the threaded section 2 and smaller thanthat of the head 3. On the end opposite to the second bore the firstbore is open and its diameter is of such a size that that the screwmember 1 can be guided through the open end by its threaded section 2going through this bore and by the head going as far as the bottom ofthe first bore. The bottom of the first bore is constructed as aspherically shaped region towards the open end, the radius beingsubstantially equal to the radius of the spherical segment-shapedsection of the head 3. Furthermore, the receiving part 5 has a U-shapedrecess 8 arranged symmetrically relative to the center of the part whosebottom is directed towards the second bore 7 and whose two side legs 13,14 extend to the open end directed towards the first bore 6. At the freeend of the legs 13, 14 a thread for engagement with a screw memberconstructed as a nut or screw is provided. The nut or screw serves tofix a rod to be inserted into the U-shaped recess 8, it being possiblefor the nut or screw to act on the rod directly or via a pressuremember.

In the embodiment shown in FIGS. 1 and 2, in the direction of the arrow9, whose direction lies in a plane going through the axis of symmetry ofthe first bore and which is inclined to the axis of symmetry by apredetermined angle, a circular countersink 10 is made in the edgebetween the opening plane 11 of the second bore and the edge 12 of thefirst bore.

In this manner, as can be seen in the figures, it is achieved that theangle between the axis of the screw member 1 and the axis of symmetry ofthe first bore is substantially enlarged by comparison with the angleotherwise attainable. At the same time the seat of the screw member 1 inthe receiving part is retained.

In the second embodiment shown in FIG. 3 the interior of the receivingpart 5 is constructed as in the first embodiment. The opening plane 11,which bounds the second bore 7, in this embodiment is inclined at apredetermined angle α to the plane bounded by the second bore 7 so thatthe normal to this plane 11 and the axis of symmetry of the first bore15 enclose the angle of inclination. In the case shown this angle is 15°as an exemplified embodiment. In this version it is also achieved thatthe screw member 1α pivotable in the direction shown by an angle to theaxis of symmetry of the-first-bore which is substantially greater thanthe angle which is achievable in the usual mode of construction.

Both in the embodiment shown in FIG. 1 and the embodiment shown in FIG.3 the countersink or chamfer is selected in such a way that in each casea small peripheral section still remains which still belongs to thespherical seat.

In a fourth embodiment which is not shown the mid-point of the secondbore is constructed offset to the side to a small extent, for example by0.5 mm, relative to the axis of symmetry of the first bore. This lateraloffsetting in turn produces the result that the head is held in themounting formed by the spherically constructed bottom but a greaterpivot width is achieved in a side direction.

In the exemplified embodiments described above four different approachesto a solution are presented. It is also possible to combine theindividual approaches with one another; that is, for example, to combinethe solution according to the first and second exemplified embodimentsor one of the two with the third and/or fourth exemplified embodiment,or even all four exemplified embodiments in order to achieve, in thisway, a still greater possibility for pivoting in at least one direction.

In the exemplified embodiments described above the spherical bottom ofthe first bore 6 is constructed in each case as an integral component ofthe receiving part 5. In a modified embodiment, however, the sphericalbottom can also be provided either in a mounting part introduced throughthe first bore 6 or in a mounting part introduced through the secondbore 7. The invention is then used in a corresponding manner to the endthat the receiving part together with the insert piece is regarded asone member and the measures described above are taken on this pieceassembled in this way.

The members forming the bone screw are preferably made of titanium.

In the embodiment shown in FIG. 4 the edge bounding the free end of thesecond bore viewed relative to the axis of the first bore is ofsymmetrical construction. The asymmetry is achieved in that the screw 1has a recess or countersink 16 on its neck engaging on the sphere or thespherical segment so that in the manner shown in FIG. 4 as in theexemplified embodiments previously described the enlarged pivot anglecan be achieved.

What is claimed is:
 1. A bone anchoring device comprising: an anchormember comprising a head; and a receiving part comprising: a top endhaving an uppermost end face defining a first plane; a bottom end havinga lowermost end face defining a second plane that intersects the firstplane; a monolithic inner surface that defines both a first bore formedat the top end and a second bore formed at the bottom end that isarranged at an angle to the first bore; wherein the second bore definesa seat adjacent the bottom end for receiving the head of the anchormember.
 2. The bone anchoring device of claim 1, wherein the head of theanchor member is curved.
 3. The bone anchoring device of claim 2,wherein the curved head comprises a spherical segment-shaped portion. 4.The bone anchoring device of claim 1, wherein the anchor member furthercomprises a bone engagement structure opposite the head for insertioninto bone.
 5. The bone anchoring device of claim 4, wherein the boneengagement structure comprises a threaded section.
 6. The bone anchoringdevice of claim 1, wherein the first bore extends from the top endtowards the bottom end and the second bore extends from the bottom endtowards the top end.
 7. The bone anchoring device of claim 6, whereinthe second bore comprises the seat.
 8. The bone anchoring device ofclaim 6, wherein a diameter of the second bore increases from the bottomend towards the top end.
 9. The bone anchoring device of claim 1,wherein the anchor member is configured to extend from the bottom end ofthe receiving part.
 10. The bone anchoring device of claim 1, whereinthe seat comprises a spherical segment-shaped portion.
 11. The boneanchoring device of claim 10, wherein the spherical segment-shapedportion of the seat increases in diameter from the bottom end towardsthe top end.
 12. The bone anchoring device of claim 1, wherein thereceiving part further defines a recess at the top end for receiving arod.
 13. The bone anchoring device of claim 12, wherein the recessextends transversely through the receiving part.
 14. The bone anchoringdevice of claim 12, wherein the recess is U-shaped.
 15. The boneanchoring device of claim 12, further comprising a locking element forlocking the anchor member and a rod relative to the receiving part. 16.The bone anchoring device of claim 1, wherein the seat decreases indiameter from the top end towards the bottom end.
 17. The bone anchoringdevice of claim 1, wherein the first bore and the second bore areconfigured to receive the anchor member.